This invention relates to an improved mold assembly for fabricating intraocular lenses. More particularly, the invention relates to disposable lens molds having novel features which permit easy alignment of the two mold halves and ensure properly finished lens edges by minimizing flash.
The use of intraocular lenses (IOLs) to improve vision and/or to replace damaged or diseased natural lenses impaired by cataracts, has obtained wide acceptance for a long period of time. Accordingly, a variety of IOLs have been developed for surgical implantation into the posterior or anterior chambers of the eye according to a patient's needs. Known IOLs comprise an optical lens portion or optic which includes an optical zone, and one or more supporting structures, called fixation members or haptics, for contacting eye tissue to fix or hold the IOL in the proper position after implantation. The optic may comprise a relatively hard or rigid material such as, for example, polymethylmethacrylate (PMMA), or, increasingly, a soft, resilient polymeric material, such as silicone or an acrylic material. The softer optic materials are advantageous in that they are deformable, e.g. foldable, so that for implantation a smaller incision may be surgically cut in the eye than for implantation of "hard" intraocular lenses.
It is known in the prior art that intraocular lenses made from soft biocompatible materials such as silicone polymers or acrylics possess desirable properties, having sufficient structural integrity, elasticity, and a small enough size to permit them to be folded for insertion through a small incision. After insertion, the soft lens is resilient enough to regain its original molded shape.
To fabricate a soft, biocompatible lens using prior art molding techniques, a polished stainless steel mold, having a mold cavity in the shape required for the correct refraction of light for the material selected, is employed. In the case of silicone, the uncured silicone polymer is introduced into the mold cavity, in an amount dictated by considerations relating to the lens size, refractive power, and structure, and allowed to cure. Several methods of molding the lens have been employed, including injection molding, liquid injection molding, compression molding, and transfer molding.
there are several significant problems associated with the above described lens molding techniques, particularly involving the employment of re-usable steel molds to fabricate the lenses. One problem is that the process is labor intensive. The silicone elastomer used to mold the lens leaves a residue in the mold, requiring cleaning of the mold between each molding cycle. Besides being labor intensive, the cleaning step results in a lot of downtime for the equipment, further increasing production costs. Another problem is that of frequent tool damage and wear because of the repeated cleanings, resulting in the need to often replace the molds, which again drives up costs and increases downtime of the equipment.
Another problem with using steel molds is one of quality control with respect to the molded lens. In contrast to contact lenses, it is imperative that an IOL have a smooth, polished edge, because of its location within a patient's eye. Improperly finished lens edges of such IOL's may result in damage to the interior structures of the eye, particularly abrasions of the iris surface and tearing of the trabecular meshwork. Unfortunately, steel, which is relatively non-compliant, typically leaves minute gaps between mold halves when they are clamped during the molding operation, due to construction tolerances. Consequently, molding material leaks out through the gaps during molding, resulting in a phenomenon known as "flash", which is unwanted attached material at the parting line (between the mold halves) on the molded lens. This flash material must be ground off and the lens edges polished in a labor intensive subsequent finishing step, again increasing production costs.
What is needed, therefore, is a new IOL mold which is inexpensive, less labor intensive, and produces a high quality IOL having smooth edges which minimizes postmolding finishing.